Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Mars Direct in 1970 ?
Date: Fri, 10 Sep 1999 14:58:15 GMT
In article <936949713.69502@avian.microgaming.com>, Frank <x@xer.com> wrote:
>>I don't *think* anyone had proposed direct launch from Earth, but with a
>>modicum of in-orbit assembly ... there were a number of reasonable
>>chemically-powered proposals.
>
>Did these proposals haul ALL the propellants and consumable all the way to
>Mars?
In general, yes. Details varied; in many cases the penalty was reduced
somewhat by using very-high-energy propellants (e.g. ClF5 as the storable
oxidizer).
>I know about von Braun's (sp?) proposal with fleets of huge nuclear
>vessels.
You're probably thinking of Das Marsprojekt, which did have a substantial
fleet but was all-chemical. (Not even very high-performance chemical,
either. But then, it was written in the early 1950s.)
>Would scavenging through the NASA websites lead to any information
>on these chemical powered proposals?
Probably not very much -- it's hard to find details on missions which were
not flown, even on paper, and this sort of obscure historical stuff is not
finding its way onto the web at any great rate. (There is too much of it,
and not much money for the conversion job.)
>>ISRU concepts actually have a long history...
>
>I understand that Zubrin's choose of fuel manufacturing process is (a)
>pretty current and (b) has the biggest 'mass leverage' going for it. Early
>proposals tended to focus on extracting either O2 or H2 out of the Martian
>enviroment or on more exotic stuff like CO rockets.
No, despite what you might see in some places, competitors are still very
much in evidence. Zubrin's H2+CO2->CH4+O2 concept, although interesting,
does have a disadvantage or three: the need to carry liquid hydrogen, the
need to refrigerate the propellants, and the high power needs.
Using CO as the fuel (with O2 as oxidizer) has higher (in principle,
infinite) mass leverage, gets rid of the LH2, and simplifies the hardware
as well. (Zubrin's favorite does not produce enough oxygen, so he ends up
needing a supplementary CO2->CO+O2 process anyway.) The performance is
somewhat lower, alas, and the refrigeration and power problems are still
there.
Taking along B2H6 or SiH4 or a powdered metal as fuel, and just using CO2
as the oxidizer, reduces performance and has unimpressive mass leverage,
but has the very large practical advantages of no refrigeration and quite
low power requirements.
In the long run, you could maybe think about getting hydrogen from local
sources, but that's harder. There is not much water vapor in the
atmosphere, and other sources remain uncertain.
Of course, the ultimate ISRU is to collect propellant for a nuclear rocket
locally. A little tricky for Mars because hot CO2 is an oxidizer, but if
you process it into CO, it should be okay. (CO has a pretty tight grip on
its oxygen atom.) Or build a special nuclear engine with materials suited
to oxidizing propellants.
>>...development of the Mars lander...
>
>How similiar would the technology used be? The mars lander is an interesting
>mix between the LEM and the CM in mission requirements. The actual
>technology for a Mars lander can't have been that ar away because the first
>Viking probe was only a couple of years around the corner (July 1975?)
Getting things *down* is not a big problem, although you have to watch the
scaling laws (Viking used parachutes, manned landers might be too big for
those to work well). Getting up off the surface is a bit harder. So are
surface operations; the environment is quite unlike the Moon in important
ways (e.g., the Apollo spacesuits are too heavy). No massive obstacles,
but a fair bit of engineering development needed.
>>Uh, no. ICs were normal commercial/industrial electronics technology by
>>1970, and were used in leading-edge space hardware much earlier...
>
>I had thought that the Apollo IC computers were one-of-a-kind super
>expensive, barely out of the lab type things, not actual commerical
>technology.
The *first* Apollo prototypes were just about in that category, although
the number of ICs they used was so large -- at one NOR gate per IC -- that
the ICs were necessarily in volume production by the time the flight
models were being built. But things changed a lot between the first
prototypes and Apollo 11. ICs were in mass commercial use by 1970.
>>Depends on exactly what you mean by "aerobraking". Apollo flew an
>>aerocapture trajectory (high-energy reentry from imitation lunar
>>trajectory) in 1967. The Soviets launched an unmanned aerocapturing Mars
>>lander in 1971 (it landed more or less intact but did not survive long).
>
>Mars Direct calls for a direct landing. No orbits or anything like that.
>This is (I expect) a pretty stiff regeme (going from 45000 kph to 0 in a
>hundred kilometers or so of very thin atmosphere. That's what I understand
>by aero-braking (I could be wrong.)
The terminology is vague; "aerocapture" is the word often used for
shedding interplanetary velocity in a single pass.
>Were the Apollo CM re-entries direct or
>did the SM-CM stack first insert itself into an orbit before de-orbiting?
Direct; the fuel requirements for anything else were prohibitive. And
the Soviet Mars 3 lander likewise went direct to the Martian surface.
>>...Skylab supported crews for a total of about six
>>months, and had enough consumables left for at least one more visit, and
>>basically used no recycling at all. A lot of work was done on recycling
>>in the 1960s, and some of it would have been practical for a Mars flight.
>
>Brute force is good, but it does tend to drive up mission mass. Once on Mars
>you can get your oxygen (and a little nitrogen) 'free' from the atmosphere.
>How reliable would 1960's recycling technology have been? Things tend to
>break down. It is best not to be half way to Mars and run out of spares.
The stuff would be tested before being used for real. (Today's NASA tends
to skimp on that step, but the 1960s NASA had more sense.) I think some
basic things like limited water recycling wouldn't have been a problem,
and that alone would give a lot of mass leverage.
>Could state-of-the-arts 1960's polymer technology have built an inflatable
>green house for Mars surface use. This could have provided some useful data
>on plant growth and helped ease the consumables requirement.
Shouldn't have been a problem, especially if it was experimental and you
didn't worry too much about long life.
>>>Might this not be solved with a little extra fuel manufactured on Mars
>>>used to slow down the ship.
>>Not really practical. You need a lot of fuel, not a little...
>
>Ok. What about gravity assists, stuff like that? Use Luna and Earth's
>gravity to slow you down.
Unfortunately, there's nothing much useful there. Lunar gravity assists
simply do not gain you very much, and they also tend to have short timing
windows. You can't use Earth's gravity to help with the job of settling
into Earth's gravity. And any scheme which involves batting around the
Earth-Moon system for a while has problems with consumables and Van Allen
belt exposure. It really is much simpler to just take something like an
Apollo CM, with just enough consumables for reentry, and go straight in.
>>>Was a small autonomeous robot rover within the reach of 1970s electronics?
>>The Mars Direct rover does not have to be either autonomous or particularly
>>small. Not a problem.
>
>It needs to be smart enough to detatch itself from the landing craft, roll
>off and deploy the reactor.
Yes, but it doesn't have to be *autonomous* -- the brains can be back on
Earth, it doesn't matter whether it takes days to do the job by remote
control. And the rover mass is a small fraction of the payload, so just
making it heavier as needed is not a big problem.
--
The good old days | Henry Spencer henry@spsystems.net
weren't. | (aka henry@zoo.toronto.edu)

From: henry@spsystems.net (Henry Spencer)
Newsgroups: sci.space.tech
Subject: Re: "Mars Flag" and Habitat, Q?
Date: Wed, 26 Jan 2000 04:31:21 GMT
In article <862ag2$kql$1@nntp9.atl.mindspring.net>,
gj bart <bronco@netcom.com> wrote:
> The above is a sumnation of Zubrin's idea, and when I heard it
>the other day it was indeed very convincing (to a layperson). But more
>interesting is what are the potential problems with the idea...
In deference to the name of this newsgroup :-), I'll skip the political
problems (which are serious) and focus on the technical ones.
Modest though it is, you can't launch it with today's launchers, so you
have to develop a new heavylift launcher. You can reduce the problems of
doing that with a shuttle-derived system, which indeed is Zubrin's
favorite line of approach, but it's still a headache.
Powering fuel production on the Martian surface is a problem. Zubrin's
preferred method is a nuclear reactor, but no suitable reactor design
exists, and the political problems of developing one are formidable.
Solar power has problems with things like dust accumulation, not a big
deal with people on the spot but a real question mark for a system which
has to operate for a year or two unmanned.
More generally, debugging the design of that fuel-production system is not
going to be simple. Yes, chemical processes do have to be debugged. We
can simulate the Martian atmospheric composition without much difficulty,
but accurate simulation of details like the dust environment is harder,
and it might matter. There is a significant chance that the first return
vehicle will be a writeoff because the fuel production system won't work
well enough. (This is a generic problem with most systems for exploiting
local resources -- people assume we can build complex processing systems
which work reliably the very first time, which historically is naive.
Even scaling up something you've tested on a small scale is not always
100% trouble-free.)
--
The space program reminds me | Henry Spencer henry@spsystems.net
of a government agency. -Jim Baen | (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.tech
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Mars: More practical, Water or CO2 for fuel?
Date: Thu, 29 Jun 2000 01:52:46 GMT
In article <395A60FE.2FBAA331@ASmit.edu>,
Jason Goodman <goodmanj@ASmit.edu> wrote:
>> Well, I would raise one small objection to this: there is an almighty lot
>> of dust in the Martian air, and quantifying the effects *that* will have
>> on things like compressors is more than slightly difficult...
>
>We don't need no stinking compressors. Zubrin suggests (Case for Mars, p. 148)
>using a zeolite or activated carbon sorbtion bed, which will absorb and release
>CO2 as it's heated and cooled. No moving parts.
It will need valves at least, because you have to alternately expose it to
the atmosphere and seal it off to extract the adsorbed gas. Some of the
adsorption designs I've seen rotated the adsorption bed in and out, too.
And of course, the bed itself can get dirty; the application *inherently*
involves a lot of air flowing into it.
Not quite as simple as it looks. Zubrin is a smart guy, but a chemical
engineer he's not, and he makes some slightly naive assumptions about
issues like dealing with contaminants. Maybe his ideas will work well
enough, but maybe not. There's only one way to find out for sure.
--
Microsoft shouldn't be broken up. | Henry Spencer henry@spsystems.net
It should be shut down. -- Phil Agre | (aka henry@zoo.toronto.edu)